In communication in a beam domain, that is, an auxiliary beam antenna is added on the basis of a conventional macrocell antenna, and the auxiliary beam antenna is combined to serve a terminal inside a sector, thereby implementing improvement of capacity performance. The essence of communication in the beam domain is to maximize gain brought by spatial dimensionality. Such superimposition of at least one auxiliary beam antenna on the basis of a conventional macrocell antenna to perform spatial multiplexing causes a critical problem, that is, how to accurately select a suitable antenna for a terminal user; that is, which antenna is to be used to serve the terminal needs to be specified before a base station (including an indoor base station and an outdoor base station) is to send data to a terminal. Therefore, a base station needs to measure downlink channel quality of a corresponding equivalent channel when each antenna serves the terminal.
A reference signal, that is, a pilot signal, is a known signal that is provided by a transmit end for a receive end and is used for channel estimation or signal measurement. In an LTE (Long Term Evolution) system, an SRS (sounding reference signal) is used for an uplink pilot, that is, a pilot signal transmitted by a terminal to a base station, and the base station acquires, according to an SRS received by each antenna, uplink channel quality of each antenna for the terminal. Generally, the base station estimates downlink channel quality by using channel interchangeability according to the measured uplink channel quality. However, for an FDD (Frequency Division Duplex) system, because uplink and downlink frequencies are different, downlink channel quality estimated by using channel interchangeability has a large error.